In optical connection using an optical adapter, a pair of ferrules having the same diameter are connected together in a form of butt joint. It is noted, however, that the standards in Japan and outside Japan for optical connectors with regard to their shapes and sizes have not yet been unified. Thus, it is sometimes necessary for a pair of ferrules of a different diameter, for example, one being of a SC type optical connector and the other being of a miniature SC type optical connector, to be connected together.
A sleeve for an optical connector for holding a pair of ferrules of a different diameter together in a coaxial fashion is disclosed, for example, in Japanese Utility Model Public Disclosure No. (Hei)03-65106 and Japanese Patent Public Disclosure No. (Hei)05-88044. The sleeve S disclosed therein includes, as shown in FIG. 3, a split sleeve 10 and a cylindrical body 11 which are inter-fitted with each other. The split sleeve 10 is finished on its inner diameter by means of precision grinding. The cylindrical body 11 is finished on its inner and outer diameters by means of precision grinding. The sleeve S is fitted into a connector housing of a cylindrical configuration and fixed therein. An optical connector having a ferrule of a larger diameter is inserted into the split sleeve 10 from the left-hand side as viewed in FIG. 3. Another optical connector having a ferrule of smaller diameter is inserted into the cylindrical body 11 from the right-hand side as viewed in FIG. 3. Each optical connector is anchored to the connector housing by means of a hook provided at each end of the connector housing.